Optical study of SrAl 1.7 B 0.3 O 4 :Eu, R ( R =Nd, Dy) pigments with long-lasting phosphorescence for industrial uses

We have studied and compared the optical properties of SrAl1.7B0.3O4:Eu, R (R=Nd, Dy) pigments that present long-lasting phosphorescence obtained by different synthesis techniques. Samples obtained by ceramic methods, in our laboratories and by an industrial process, present better phosphorescent properties than those obtained by sol–gel technique. Raman spectra show that grinding produces severe damage of the lattice. We have obtained and analyzed the Eu3+ crystal field luminescence indicating that Eu3+ is found in quite different sites comparing ceramic and sol–gel samples. Codoping, with Nd or Dy is necessary in order to reduce the Eu3+ content, in all cases. The green luminescence band, obtained under UV illumination, can be fitted to two and three components in ceramic and sol–gel samples, respectively, due to different Eu2+ sites. Eu–Dy samples present the longest and the most efficient phosphorescence. The time evolution of the afterglow is well described by a t−1 law, up to about 2 h, indicating that the recombination process is achieved by electron–hole tunneling.